1. Field of the Invention
The present invention relates to a method for estimating the steering wheel angle position of a vehicle based upon data received from a relative position steering angle sensor and other vehicle sensors.
2. Description of the Related Art
Many vehicles today have electronic controllers which utilize data signals obtained from a Steering Angle Sensor (xe2x80x9cSASxe2x80x9d) to make complex calculations and automatically implement actions based upon those calculations. There are different classes of SAS sensors. Class III sensors provide accurate values immediately after the ignition key is placed in the ON condition.
Class I SAS sensors provide values which are relative to the position of the steering wheel when the ignition key is turned to the ON condition. In other words, these sensors transmit a zero value signal when the key ON condition is initiated regardless of the actual steering wheel position and processing of the SAS signal is required to compute an accurate steering wheel angle value. A variety of different methods are known for processing the relative position SAS sensor signal to estimate the actual steering wheel angle.
The present invention provides an improved system for estimating the actual steering wheel angle position based upon signals received from a relative position steering angle sensor and other vehicle sensors for measuring various vehicle operating parameters.
The invention comprises, in one form thereof, a method of estimating the true steering angle of a vehicle. The method includes obtaining a relative position steering angle value, obtaining a plurality of vehicle operating parameter values, and calculating a plurality of estimated values wherein each of the values is a function of one of a plurality of different vehicle models and each of the vehicle models includes at least one variable corresponding to one of the plurality of vehicle operating parameter values. The method also includes estimating a steering angle offset value as a function of a weighted average of the plurality of estimated values and estimating the true steering angle value of the vehicle as a function of the relative position steering angle value and the steering angle offset value.
The plurality of different vehicle models may include a yaw rate model, e.g., equation (1), having a variable corresponding to a yaw rate of the vehicle, a lateral acceleration model, e.g., equation (3), having a variable corresponding to a lateral acceleration of the vehicle, a front axle model, e.g., equation (4), having variables corresponding to a front left wheel speed value and a front right wheel speed value, and a rear axle model, e.g., equation (5), having variables corresponding to a rear left wheel speed value and a rear right wheel speed value.
Alternatively, the plurality of different vehicle models may include at least two models selected from the group including a yaw rate model, a lateral acceleration model, a front axle model and a rear axle model. The step of obtaining a plurality of vehicle operating parameters may include obtaining a sensor-measured yaw rate of the vehicle when the yaw rate model is one of the selected models with the yaw rate model having a variable corresponding to the sensor-measured yaw rate. The step of obtaining a plurality of vehicle operating parameters may include obtaining a sensor-measured lateral acceleration of the vehicle when the lateral acceleration model is one of the selected models with the lateral acceleration model having a variable corresponding to the sensor-measured lateral acceleration. The step of obtaining a plurality of vehicle operating parameters may include obtaining a left front wheel speed value and a right front wheel speed value of the vehicle when the front axle model is one of said selected models with the front axle model having variables corresponding to the left front wheel speed value and the right front wheel speed value. The step of obtaining a plurality of vehicle operating parameters may include obtaining a left rear wheel speed value and a right rear wheel speed value of the vehicle when the rear axle model is one of said selected models with the rear axle model having variables corresponding to the left rear wheel speed value and the right rear wheel speed value.
The step of estimating a steering angle offset value as a function of a weighted average of the plurality of estimated values may involve unequally weighting at least two of the plurality of estimated values, e.g., equation (6) wherein C1, C2, C3 and C4 are not all equal. The estimation of the true steering angle value may also be a function of an uncertainty factor wherein the uncertainty factor is a function of a minimum value and a maximum value of the estimated values, e.g., equations (8), (9) and (10).
The method may also include repetitively performing the step of estimating a steering angle offset value and defining a mode value of the method wherein the mode value is a function of the number of calculated steering angle offset value estimates. The mode value and all changes in the mode value are communicated to a controller.
The method may also include the step of selecting data acceptable for use in estimating the steering angle offset value wherein the step of selecting data includes accepting for use data obtained when the sign of a sensor-measured yaw rate of the vehicle (vGimeas) is the same as a model-based yaw rate (vGiVr) calculated using front and rear axle operating parameters; and also accepting for use data obtained when the sign of vGimeas is opposite the sign of vGiVr when relatively straight rearward driving is detected. The detection of relatively straight rearward driving may be defined as when Fk+1 greater than W3 and Fk+1=(Fk*W1+(vGiVr*vGimeas))/((vGiVr)2+(W1+W2)) wherein Fk is a formulation variable and W1, W2, and W3 are all constants. In one embodiment of the invention, W1 may be defined as a value which is approximately 0.05; W2 may be defined as a value which is approximately 0.80; and W3 may be defined as a value which is approximately xe2x88x920.3.
The invention comprises, in yet another form thereof, a method of estimating the true steering angle value of a vehicle. The method includes obtaining a relative position steering angle value, obtaining at least one vehicle operating parameter value, and calculating at least one estimated value wherein the estimated value is a function of a vehicle model including at least one variable corresponding to the at least one vehicle operating parameter value. The method also includes estimating a steering angle offset value as a function of the estimated value, estimating the actual steering angle value of the vehicle as a function of the relative position steering angle value and the steering angle offset value and, prior to estimating the steering angle offset value, selecting data acceptable for use in estimating the true steering angle value wherein data acceptable for use includes both data obtained when the sign of a sensor-measured yaw rate of the vehicle (vGimeas) is the same as a model-based yaw rate (vGiVr) calculated using front and rear axle operating parameters and data obtained when the sign of vGimeas is opposite the sign of vGiVr when relatively straight rearward driving is detected.
The detection of relatively straight rearward driving may be defined as when Fk+1 greater than W3 and Fk+1=(Fk*W1+(vGiVr*vgimeas))/((vGiVr)2+(W1+W2)) wherein Fk is a formulation variable and W1, W2, and W3 are all constants. In one embodiment of the invention, WI may be defined as a value which is approximately 0.05; W2 may be defined as a value which is approximately 0.80; and W3 may be defined as a value which is approximately xe2x88x920.3.
The invention comprises, in still another form thereof, a method of estimating the true steering angle value of a vehicle. The method includes: (a) obtaining a relative position steering angle value; (b) obtaining at least one vehicle operating parameter value; (c) calculating at least one estimated value, the estimated value being a function of a vehicle model including at least one variable corresponding to the at least one vehicle operating parameter value; (d) estimating a steering angle offset value as a function of the estimated value; (e) estimating the true steering angle value of the vehicle as a function of the relative position steering angle value and the steering angle offset value; (f) repeating steps (a) through (e) and assigning a Percent Certainty value to each estimated true steering angle value, the Percent Certainty value being a function of the number of repetitions of steps (a) through (e); and (g) communicating the estimated true steering angle value and the Percent Certainty value to a controller.
Step (c) may also include calculating a plurality of estimated values using a plurality of different vehicle models and calculating an uncertainty factor as a function of a minimum value and a maximum value of the estimated values. The Percent Certainty value may be a function of the number of repetitions of steps (a) through (e) and the uncertainty factor. The plurality of different vehicle models may include at least two models selected from the group including a yaw rate model, a lateral acceleration model, a front axle model and a rear axle model. The method may also include defining a mode value of the method wherein the mode value is a function of the number of repetitions of steps (a) through (e), and communicating the mode value and all changes in the mode value to a controller.